Well known corrugators use two series of opposed mold blocks which cooperate to define a moving mold tunnel for forming of plastic corrugated pipe. Basically the mold tunnel is aligned with an extruder to receive and shape the molten plastic to form the pipe with the moving mold blocks defining the outer surface of the plastic pipe and cooling the pipe. The series of mold blocks are typically vertically opposed having top and bottom mold blocks or horizontally opposed having left and right mold blocks.
In corrugators of this type, the mold blocks of a first series of mold blocks cooperate with opposed mold blocks of a second series of mold blocks to collectively define the inlet to the moving mold tunnel, the moving mold tunnel and the exit of the moving mold tunnel. The extruded pipe moves with the moving mold tunnel and the mold tunnel is of sufficient length to provide the required time to draw the plastic against the walls of the mold blocks and to partially cool and set the plastic prior to the mold blocks separating at the exit of the moving mold tunnel.
In the manufacture of corrugated pipe, particularly large diameter corrugated pipe, the mold blocks are displaced outwardly away from the longitudinal axis of the moving mold tunnel several times the height of the corrugations of the pipe, before the mold blocks can be rotated to avoid striking any formed corrugations.
Traditional corrugators have a shallow outwardly angled diverging portion at the exit of the moving mold tunnel which provides an angled transition region that progressively separates the adjacent pairs of the mold blocks until the end mold block is sufficiently clear of the formed product that it can be rotated and returned to the inlet of the moving mold tunnel. This angled section slowly moves the mold blocks away from the center line of the mold tunnel over a substantial distance. For example, this angled transition section can be of a length in the range of 5 to 10 mold blocks before sufficient clearance away from the product is obtained and rotation of the mold block can occur.
The present invention is directed to a method and apparatus that provides more effective use of the total number of mold blocks of a mold tunnel relative to the actual time the mold blocks are defining the mold tunnel. With this arrangement less mold blocks are required for a given length of the mold tunnel. The arrangement has particular application with respect to a mold tunnel having opposed mold blocks designed for producing corrugated pipe. On large pipe corrugators, the present arrangement can almost double the molding tunnel using the same number of mold blocks. With this longer molding tunnel the output can be dramatically increased as long as the existing extruder is not running out of capacity. A longer mold tunnel allows a corrugator to run at a higher speed while still forming and sufficiently cooling the molded product.